Medical ventilator including a fail-safe device

ABSTRACT

A time-cycled medical ventilator which includes a source of respiratory gas and hermetically driven bellows for supplying required pressure to move the gas to the patient. Operating means driven by a driving gas under control of control means operates to distend and compress the bellows in accordance with the time cycle. An inspiratory gas valve is connected on its inlet side to the source of respiratory gas for controlling the flow of gas to the patient through an inspiration gas passage. An expiratory gas valve is connected by an expiration gas passage to the patient for controlling flow of respiratory gas away from the patient. Electrically driven valve operating means are connected to each of the gas valves for controlling their operation. A pressure relief valve is connected to the inspiration gas passage so as to provide venting to atmosphere of said gas passage in order to relieve excess gas pressure from said gas passage when the gas pressure therein reaches a predetermined value. Detecting means are arranged responsive to the driving gas pressure so that when the driving gas pressure falls to atmospheric pressure means connected to said pressure relief valve will be operated to open said valve and provide a connection from atmosphere to said inspiration gas passage so as to allow the patient to breathe independent of the ventilator.

Ilnited States Patent 91 Smythe I 51 Get. 29, 1974 1 MEDICAL VENTILATOR INCLUDING A FAIL-SAFE DEVICE [75] Inventor: George Edward Smythe, Wallington,

England [73] Assignee: U.S. Philips Corporation, New

York, N.Y.

[22] Filed: Aug. 18, 1972 [21] Appl. No.: 281,720

[30] Foreign Application Priority Data Primary ExaminerRichard A. Gaudet Assistant ExaminerG. F. Dunne Attorney, Agent, or Firm-Frank R. Trifari [57] ABSTRACT A time-cycled medical ventilator which includes a source of respiratory gas and hermetically driven bellows for supplying required pressure to move the gas to the patient. Operating means driven by a driving gas under control of control means operates to distend and compress the bellows in accordance with the time cycle. An inspiratory gas valve is connected on its inlet side to the source of respiratory gas for controlling the flow of gas to the patient through an inspiration gas passage. An expiratory gas valve is connected by an expiration gas passage to the patient for controlling flow of respiratory gas away from the patient. Electrically driven valve operating means are connected to each of the gas valves for controlling their operation. A pressure relief valve is connected to the inspiration gas passage so as to provide venting to atmosphere of said gas passage in order to relieve excess gas pressure from said gas passage when the gas pressure therein reaches a predetermined value. Detecting means are arranged responsive to the driving gas pressure so that when the driving gas pressure falls to atmospheric pressure means connected to said pressure relief valve will be operated to open said valve and provide a connection from atmosphere to said inspiration gas passage so as to allow the patient to breathe independent of the ventilator.

7 Claims, 1 Drawing Figure Do B1 82 g 2 51 /V\ E :1 NRV4 3T1 T L Dc1 At I l 2 S2 2 NRV5 g M R6 MEDICAL VENTILATOR INCLUDING A FAIL-SAFE DEVICE This invention relates to time-cycled medical ventilator and more particularly to such a ventilator including a fail-safe device operable in the event of failure of the ventilator control arrangement.

In time-cycled ventilators, respiratory gas is passed to a patient during each inspiratory period via an inspiratory valve in an inspiration gas passage and from a patient during each expiratory period via an expiratory valve in an expiration gas passage. These valves are operated alternately by control equipment to regulate inspiration and expiration in accordance with a predetermined time cycle.

If part or whole of the respiration control equipment should fail due, for example to a faulty control valve or to failure of the mains power supply, either or both of the inspiratory and expiratory gas passages to the patient may be blocked by the appropriate valve for a lengthy period.

In many cases of lung ventilation, the patient has an inherent breathing capability even if a limited ability. The object of the present invention is the provision of a medical ventilator including a fail-safe device which overcomes the above disadvantage and allows a patient to breathe freely in case of ventilator failure.

According to the present invention there is provided a time-cycled medical ventilator including:

' inspiratory and expiratory gas valves for controlling flow of respiratory gas to and from a patient, respectively, via inspiration and expiration gas passages,

pneumatically-driven operating means associated with each phase of the respiration cycle, driving bellows B1 and B2 control means for controlling flow of driving gas at higher than atmospheric pressure to the valve operating means so as to cause the latter to distend and compress the bellows alternately in accordance with the time cycle,

a pressure relief valve associated with the inspiration passage on the patient side of the inspiratory gas valve and of a flow rate control valve if such be fitted and arranged to open if the pressure in the said passage exceeds a predetermined level so as to vent the passage to atmosphere and so relieve the excess pressure, and

detecting means responsive to the pressure of the driving gas and arranged to open the pressure relief valve if the pressure of the driving gas drops to atmospheric level for a period in excess of a respiratory cycle.

By providing a detecting means which is sensitive to the pressure of driving gas, and which operates a pressure relief valve in the inspiratory gas passage if the driving gas pressure falls to atmospheric level i.e. when it is no longer a driving gas since it cannot operate the bellows the patient is able to inhale freely via the opened relief valve. This is advantageous even if the inspiratory valve is not closed under the fault condition because the ventilator includes a restriction in the respiratory gas flow path in the form of a flow rate control. By locating the relief valve on the patient side of the inspiratory valve and of the flow rate control valve, these are by-passed and the patient can inhale freely.

According to a preferred embodiment of the invention, an additional safety device is provided in that the expiratory gas control valve is provided with a spring which opens the valve automatically if the normally applied valve operating means fails. By ensuring that the expiratory valve is also opened in the event of ventilator failure, the patient is provided with a clear exhalation path.

The various features and advantages of the present invention will be apparent from the following description of an exemplary embodiment thereof, taken in conjunction with the accompanying drawing which shows schematically the driving and respiratory gas circuits of a respirator according to the invention.

Referring now to the drawing, in which respirator gas passages are shown as pipelines and driving gas paths are shown as single lines, two solenoid-operated gas control valves S1 and S2 are shown in the customary symbolic form, the right hand portion representing the solenoid, the zigzag to the left indicating that it is a spring-returned solenoid, the left-hand square showing the gas passage path with the solenoid in the unoperated condition and the right-hand square showing the gas passage path with the solenoid operated, the righthand square replacing the left-hand square in this condition. lnlet ports of these solenoids are connected at inlet DG to a source of driving gas at higher than atmospheric pressure, e.g. compressed air.

Ports 1 of valves S1 and S2 are connected to the driving gas source DG, ports 2 are connected to ports of pneumatically-operated driving cylinder DC 1, and containing an actuating piston and ram, and ports 3 are connected to the atmosphere At via silencing devices (not shown) if required.

The respiratory gas circuit includes, on the inspiratory side, a respiratory gas inlet R6 for gas (e.g. clean air) at atmospheric pressure, non-return valves NRVl and NRV2, and inspiratory valve IV actuated by solenoid DSl, bellows B1 and B2 which can be expanded and contracted by the piston and ram of cylinder DC 1, and a flow rate control FRC (a variable constriction, for example). On the expiratory side, gas is passed from the patient via an expiratory valve EV and a non-return valve NRV3 to atmosphere (At).

Solenoid valve 81 is operated during the inspiration period and solenoid valve S2 is operated during at least part of the expiratory period by means of conventional time control circuits.

Assume initially, that valve S1 is operated and that the bellows B1 and B2 are filled with the required volume of respiratory gas to be passed to the patient. Driving gas from inlet D6 is passed via ports 1 and 2 of valve S1 (operated) to the upper chamber of driving cylinder DCl thus forcing the piston and ram downwards and hence contracting the bellows to expel the contained volume of respiratory gas. At the same time solenoid DS! is de-energised thus allowing the inspiratory valve IV to open under the force of the spring; Respiratory gas is now expelled, under pressure of the driving gas, from the bellows at a rate determined by the setting of the flow rate control FRC, thus opening non-return valve NRVZ, to the Y-piece of the face mask or respiratory tube. The pressure in the inspiratory airway holds non-return valve NRVl closed, this pressure being higher than the atmospheric pressure of the respiratory gas on the other side of the valve.

During the inspiratory period, expiration valve EV is held closed by solenoid DSZ which is energised during the inspiration period. This ensures that none of the respiratory gas can escape via the expiratory path. An escape path for the gas driven out of the non-driving chamber of cylinder DC]. during movement of the piston is provided via ports 2 of the cylinder and valve S2 (unoperated) to atmosphere.

At the end of the inspiratory period, valve S1 releases and valve S2 is operated. Under this condition, driving gas is fed to port 2 of cylinder DCl, and a venting path to atmosphere is provided via port l and valve SI (unoperated).

The operation of the piston of cylinder DCI in the upwards direction now causes the pressure in bellows B1 and B2 to be reduced, thus opening non-return valve NRVR and drawing respiratory gas into the bellows via inlet RG. lnspiratory valve IV is closed by the solenoid D81 and the expiratory valve EV is opened under its spring pressure since the solenoid D82 is now de-energised by the electrical control device.

The pressure in the patients lungs is higher than atmospheric pressure so non-return valves NRV2 and NRV3 are closed and opened respectively, thus enabling the gas in the patients lungs to be vented to atmosphere via the Y-piece, hose line HL, expiratory valve EV (open), and non-return valve NRV3 (open) to atmosphere.

During the expiration period, the bellows B1 and B2 are filled with respiratory gas under the control of driving cylinder DCl, until the required tidal volume has been stored, ready for passage to the patient during the next-following inspiration period.

A blow of type pressure safety valve is associated with the inspiratory gas passage on the patient side of the inspiratory valve IV and the flow rate control FRC. This safety valve comprises a valve member VM held in gas-tight relationship with a valve seat VS by means of a weight W adjustably disposed, on a lever arm LA pivotted at point P by a pivot, the lever arm being coupled with the valve member so as to bear thereon with a force depending upon the position of the weight W along the arm. This is a well-known type of safety valve. The position of the weight W is set according to a safe maximum permissible lung pressure for the patient concerned. If this pressure is exceeded for any reason due to faulty ventilator operation, the excess pressure above the safe maximum blows off" the valve member and the excess pressure in the inspiratory passage is relieved to the atmosphere.

In accordance with the invention, this safety valve is operated if the control system of the ventilator fails, for example by failure of solenoids S1 and S2 to operate, such that no driving gas is passed to the drive cylinder. This is achieved by a detecting means, responsive to the pressure of the driving gas, comprising non-return valves NRV4 and NRVS, connected to the respective driving gas outputs of ports 2 of solenoids S1 and S2, a gas flow-restricting device FR, and a variable capacity gas reservoir GR. Reservoir GR comprises a cylinder having a piston and piston rod slidably arranged therein, the variable capacity being formed by the volume above the piston. A spring is provided which acts on the piston to drive it upwards and reduce the capacity to a minimum if the gas pressure in the capacity falls below a given value. The volume in the cylinder below the piston is vented to atmosphere as shown so as to enable the piston to move freely.

For convenience, the piston is shown in the position providing the maximum capacity, the spring being compressed so that its pressure exerted on the lower face of the piston is equal and opposite in direction to the pressure exerted on the upper face of the piston by the contained .gas. The variable capacity GR is provided with a gas discharge path to atmosphere via a gas flow restricting device FR. With the variable capacity fully charged with gas at the pressure of the driving gas, and assuming for the moment that no driving gas is fed to the variable capacity to maintain it at its maximum capacity, the pressure in the capacity slowly reduces towards atmospheric pressure due to escape of gas via the flow restrictor FR. As the pressure in the capacity reduces, so the piston is moved in the upward direction by the spring.

It will be readily appreciated that the capacity and restrictor form a time constant circuit having a time constant dependent upon the volume of the capacity and the flow rate via restrictor FR. In practice, restrictor FR is adjusted so that the time constant exceeds the duration of a respiratory cycle; this time constant be ing, for example, in the order of five seconds.

At the end of the time constant period this piston rod engages lever arm LA and moves it upward; so opening the safety valve and venting the inspiratory gas passage to atmosphere. The valve seat VS is provided with a large diameter such that only a small opening of the valve is required for an adequate supply of air to be drawn through the safety valve and non-return valve NRV2 by the patient.

In operation of the ventilator, driving gas passes either through non-return valve NRV4 or through nonreturn valve NRVS, according to the respiratory cycle period concerned, and charges the variable capacity of gas reservoir GR. Non-return valves NRV4 and NRVS offer very little flow resistance to the passage of gas in their operative direction and so the variable capacity charges rapidly. Since the discharging time constant of the capacity and flow restrictor greatly exceeds the charging time constant via a respective non-return valve, the capacity is maintained in the charged state during normal time-cycling of the ventilator.

If solenoids SI and S2 fail to operate, however, the capacity slowly discharges and, after the discharge time constant, the safety valve is opened. In this way the pa tient is able to inhale freely via the safety valve a few seconds after failure of the ventilator without having to draw respiratory gas solely through the higher resistance path via flow rate control FRC, inspiratory valve IV, and non-return valve NRVl. Similarly, should the source of driving gas DG fail, the valve will again be opened at the end of the discharging time constant period of GR.

Although the above-mentioned fail-safe system would function perfectly well with capacity-charging gas being derived from only one of the two driving gas paths, it is preferred to use double-sourcing via the two non-return valves to reduce piston movement of gas reservoir GR during operation and to enhance the safety of operation.

The inspiratory and expiratory valves IV and EV are of the spring restoring type and their respective driving solenoids act against these springs to close the valves. In the event of failure of solenoids DSl and D52 to operate, there is no longer a force tending to close IV or EV. Whichever of the two respiration valves is closed at the moment of failure is now opened by the action of its spring against the (now non-resisting) armature of the driving solenoid. In this way, a further safety feature is provided. On the inspiratory side of the system, the respiratory gas path is opened, thus providing a respiratory gas path to the patient additional to that via the safety valve (so covering against failure of the latter as well as providing the additional source and hence, reduced breathing effort on the part of the patient). On the expiratory side, the opening of the expiratory valve EV ensures that the patient can exhale freely via nonreturn valve NRV3. Provision of these valves NRV2 and NRV3 ensures that the patient cannot re-breath stale gas contained in the patient tubing l-lLl HLZ but is able to obtain during inspiration fresh gas uncontaminated by exhalation products of previous expiratory cycles.

I claim:

1. A time-cycled medical ventilator comprising a source of respiratory gas to be supplied to a patient, pneumatically driven bellows connected to said source of respiratory gas for supplying the pressure required to move said respiratory gas into the lungs of the patient, operating means connected to said bellows for causing said bellows to alternately distend and compress in accordance with the time cycle, control means connected to said operating means for controlling flow of driving gas in accordance with said time-cycle to said operating means to effect operation thereof, a source of driving gas for supplying said driving gas at higher than atmospheric pressure to said control means, an inspiration gas passage for supplying respiratory gas to a patient, an inspiratory gas valve connected on an inlet side thereof to said source of respiratory gas for controlling the flow of respiratory gas to the patient through said inspiration gas passage connected on the outlet side of said inspiratory gas valve, an expiration gas passage for receiving respiratory gas from a patient, an expiratory gas valve connected on the inlet side thereof to said expiration gas passage for controlling flow of respiratory gas from the patient, electrically driven valve operating means connected to each of said gas valves for controlling operation thereof, a pressure relief valve connected to said inspiration gas passage on the outlet side of said inspiratory gas valve arranged for opening so as to vent said passage to atmosphere and relieve excess pressure in said inspiratory gas passage when the gas pressure therein reaches a predetermined value, detecting means responsive to the pressure of said driving gas, means connected to said detecting means for opening said pressure relief valve when the pressure of said driving gas drops to atmospheric pressure for a period of time in excess of a predetermined period so as to connect said inspiration gas passage to the atmosphere and allow the patient to breathe independent of the ventilator.

2. The medical ventilator according to claim 1 further comprising a spring connected to said expiratory gas control valve for opening said valve when said valve operating means is not driven.

3. The medical ventilator according to claim 1 further comprising at least one non-return valve connecting said detecting means to said driving gas allowing passage of driving gas to said detecting means only when said driving gas pressure is above atmospheric pressure, said detecting means including a pneumatic time constant device which is chargeable by the driving gas passed to said detecting means by said nonreturn valve.

4. The medical ventilator according to claim 3 wherein said time constant device includes an expansible chamber for receiving and storing driving gas passed by the non-return valve, and a gas discharge path arranged to discharge gas from the chamber at a rate slower than the rate at which driving gas can be fed to the chamber via the non-return valve.

5. The medical ventilator according to claim 4 wherein said means connected to said detecting means for opening said pressure relief valve comprises mechanical linkage to said pressure relief valve so that said pressure relief valve is opened when the chamber is fully discharged of gas.

6. The medical ventilator according to claim 5 wherein said chamber comprises a cylinder having a spring-restored piston therein so that driving gas admitted to the cylinder drives the piston against the restoring force of the spring, and wherein said mechanical linkage comprises a piston rod, carried by said piston arranged to open the pressure relief valve when the driving gas is fully discharged from the cylinder.

7. The medical ventilator according to claim 1 wherein said control means comprises at least one solenoid-operated control valve. 

1. A time-cycled medical ventilator comprising a source of respiratory gas to be supplied to a patient, pneumatically driven bellows connected to said source of respiratory gas for supplying the pressure required to move said respiratory gas into the lungs of the patient, operating means connected to said bellows for causing said bellows to alternately distend and compress in accordance with the time cycle, control means connected to said operating means for controlling flow of driving gas in accordance with said time-cycle to said operating means to effect operation thereof, a source of driving gas for supplying said driving gas at higher than atmospheric pressure to said control means, an inspiration gas passage for supplying respiratory gas to a patient, an inspiratory gas valve connected on an inlet side thereof to said source of respiratory gas for controlling the flow of respiratory gas to the patient through said inspiration gas passage connected on the outlet side of said inspiratory gas valve, an expiration gas passage for receiving respiratory gas from a patient, an expiratory gas valve connected on the inlet side thereof to said expiration gas passage for controlling flow of respiratory gas from the patient, electrically driven valve operating means connected to each of said gas valves for controlling operation thereof, a pressure relief valve connected to said inspiration gas passage on the outlet side of said inspiratory gas valve arranged for opening so as to vent said passage to atmosphere and relieve excess pressure in said inspiratory gas passage when the gas pressure therein reaches a predetermined value, detecting means responsive to the pressure of said driving gas, means connected to said detecting means for opening said pressure relief valve when the pressure of said driving gas drops to atmospheric pressure for a period of time in excess of a predetermined period so as to connect said inspiration gas passage to the atmosphere and allow the patient to breathe independent of the ventilator.
 2. The medical ventilator according to claim 1 further comprising a spring connected to said expiratory gas control valve for opening said valve when said valve operating means is not driven.
 3. The medical ventilator according to claim 1 further comprising at least one non-return valve connecting said detecting means to said driving gas allowing passage of driving gas to said detecting means only when said driving gas pressure is above atmospheric pressure, said detecting means including a pneumatic time constant device which is chargeable by the driving gas passed to said detecting means by said non-return valve.
 4. The medical ventilator according to claim 3 wherein said time constant device includes an expansible chamber for receiving and storing driving gas passed by the non-return valve, and a gas discharge path arranged to discharge gas from the chamber at a rate slower than the rate at which driving gas can be fed to the chamber via the non-return valve.
 5. The medical ventilator according to claim 4 wherein said means connected to said detecting means for opening said pressure relief valve comprises mechanical linkage to said pressure relief valve so that said pressure relief valve is opened when the chamber is fully discharged of gas.
 6. The medical ventilator according to claim 5 wherein said chamber comprises a cylinder having a spring-restored piston tHerein so that driving gas admitted to the cylinder drives the piston against the restoring force of the spring, and wherein said mechanical linkage comprises a piston rod, carried by said piston arranged to open the pressure relief valve when the driving gas is fully discharged from the cylinder.
 7. The medical ventilator according to claim 1 wherein said control means comprises at least one solenoid-operated control valve. 